6.5mm Grendel: The Round the Military Ought to Have

After almost two hours of discussing the long, tortured, and circuitous development and production history of the 6.5mm Grendel, I finally came right out and asked developer Bill Alexander if he thought the Grendel would ever get a shot at replacing the much-maligned 5.56x45mm NATO cartridge.

“Who knows?” Alexander asked rhetorically, knowing there is no clear-cut, defined path to adoption by regular U.S. military units. “It’s not about good weapons and ammunition any more, it’s a political game.”

After leaving the British defense industry and setting up shop at Radford Arsenal in Virginia, Alexander spent his time designing rifles and cartridges for Americans, not studying the procurement process.

If there were a clearly defined process, it could be upset at any point by meddlesome politicians, defense department bureaucrats, or the odd general. Despite the vagaries of the military’s equipment selection process, a quick analysis shows that the 6.5 Grendel is a legitimate contender to replace the entire M4/M16A2 family of rifles, including the SDM-R and SAM-R rifles, the M14-based family of enhanced battle/squad designated marksmen rifles, and the M110 sniper/squad designated marksman rifles. And it could be accomplished with two different uppers and loads.

Since it snuck onto the scene back in 2004, the 6.5mm Grendel has quietly built a devoted following of shooters who like to do just about everything with one cartridge that will fit in an AR-15. It has also generated its fair share of controversy, from who actually developed the Grendel to quarrelsome trademark agreements.

“The .50 Beowulf was our first project, and then we did another rifle in 5.45x39mm and could not give the bloody things away,” Alexander said. “The Grendel came along in 2003 after kicking the idea along for a couple years. It really started as an amusing wildcat. The .50 was a 200-yard gun at best, and I was looking for something with more legs, something you could hunt whitetails with.”

The original Grendel concept, based on the 6.5mm PPC case, was certainly not the only 6.5mm wildcat floating around, and Bill Alexander certainly was not the only guy working on an AR-compatible cartridge. Arne Brennan’s 6.5mm wildcat was very similar to the Grendel—Alexander and Brennan compared notes on their projects from time to time—and he can be credited with a tremendous amount of development work in the 6.5mm AR arena.

Alexander did finalize the dimensions for what became the Grendel case, chamber, and throat after working closely with ballisticians from Lapua, notably Janne Pohjoispaa.

“From the PPC cartridge we kept the 30-degree shoulder angle, but shortened the neck and increased the neck thickness,” Alexander said. “We also ended up keeping the small primer and flash hole because that’s what Lapua was using in the .220 Russian brass, which is what we made Grendel brass from. After we finalized the dimensions, the Grendel stopped being an interesting wildcat and turned into a production cartridge.”

Alexander trademarked the name and specs soon after so the Grendel would not be bastardized out of existence, a fate that has befallen several other cartridges lacking the backing of a major ammunition manufacturer.

“The first 300 cases were carried over in the suitcases of Lapua reps arriving for the 2004 SHOT Show,” Alexander said. “I started trying loads and got an inkling of what we had. The Grendel was more flexible and shot better than I ever hoped and wasn’t the pain in the butt I thought it would be.”

Quite a few other AR manufacturers soon realized the Grendel’s potential, but the trademark was the source of a lot of gun industry acrimony. All of this is now a moot point—Hornady sponsored the cartridge’s submission to SAAMI early last year, and now the Grendel is a cartridge available to the masses, sort of.

“We have certainly seen our share of boom and bust, but quite a few rifle and ammo companies are starting to realize the Grendel’s potential,” Alexander said.

Other Intermediate Cartridges
What makes the 6.5 Grendel better for general military operations than all the other intermediate AR cartridges? Nothing can match the Grendel’s range. Cartridges such as the 6.8mm SPC and .300 Blackout are 300- or 400-yard cartridges at best. The Grendel is a 500-plus-yard cartridge. Bullets are the key.

“When Remington introduced the 6.8 SPC at SHOT the same year as the Grendel, we thought we were going to get exterminated,” Alexander said. “But they couldn’t have handed it to us on a plate any better. We really only started showing up in magazines and such when writers compared us to the SPC. The results really spoke for themselves. Otherwise no one would have ever heard of us.”

The 6.5mm hits a ballistic sweet spot for optimal bullet flight, much more so than the squat, fat bullets used by other cartridges. Most 6.5mm bullets higher than 100 grains start with ballistic coefficients of more than .400, something a 110-grain 6.8mm bullet (.360 BC) or 125-grain .300 Blackout bullet (.153 BC) could never hope to match.

To its credit, the .300 Blackout is much easier to suppress with 200-grain and up bullets, and it works well in PDW-length uppers. Most importantly, the Blackout uses 5.56mm magazines. The 6.8mm SPC has a little more case taper and is theoretically more reliable, but from an external ballistics standpoint, the Grendel is far superior to both.

The Grendel in Uniform
Alexander had some very simple answers when I asked him what the Grendel would look like in uniform. The entire suite of carbines, standard service rifles, and designated marksmen rifles—and that adds up to dozens of models in two calibers, 5.56×45 and 7.62×51 NATO—could be replaced by just two rifles and two bullet weights.

Despite what’s been said on the Internet, the M4 is one of the most popular infantry arms in U.S. military history, getting pretty favorable marks from combatants. So why would you want to replace it? One of the few complaints has been battlefield lethality, and most of those problems can be attributed to ammunition. The M855 Penetrator, or green tip round, was designed to defeat body armor at extended ranges. A better ammo option for now exists in the 62-grain SOST round among others, but bigger is usually better, especially if it fits in the same compact and reliable rifle. Soldiers are having trouble dominating the battlefield past 300 or 400 yards.

Alexander theorized the perfect replacement would be an M4 chambered in 6.5 Grendel with the same, handy 14.5-inch barrel and 107- to 110-grain FMJ projectiles constructed along the lines of the old Soviet 7N6 or 7N10 penetrator round. According to Alexander’s data, the 107-grain Sierra MatchKing and 108-grain Lapua Scenar cruise along at 2,500 to 2,520 fps out of M4-length barrels and have much improved BCs and mass over any 5.56mm round.

Testing showed Grendel bullets shed an average of 6 fps per inch when dropping from 28 inches down to 20 inches and 23 fps per inch when dropping from 20 to 14.5 inches. While 5.56mm bullets are just that much more ineffective out of shorter barrels, the Grendel’s efficiency and increased mass make it a more efficient killer.

Because of its length and rear weighting, the theoretical 6.5 Grendel general service round would yaw and cause significant wounding at extended ranges or up close. With a BC well above .400—the 108-grain Scenar has a BC of .465—it would crush the 5.56 and extend the average infantryman’s effective range beyond 500 yards. Seeing the target well enough to hit it becomes the issue, not terminal performance.

The squad designated marksman is a Soviet concept, borrowed by the U.S. military in Iraq and Afghanistan. Integrating a soldier or marine with extra training and an accurized, scoped rifle into infantry squads has paid big dividends. The marksmen help direct fires, identify threats, and engage targets well beyond the effective range of infantrymen equipped with standard rifles. The services have used both highly modified M16s and pulled the M14 out of retirement to meet the challenge.

M16 rifles generally were equipped with heavy, 1:8-twist match barrels around 20 inches in length and, when possible, paired with excellent Mk 262 Mod 1 ammo. The 77-grain BTHP has the most stringent accuracy standard of any small arms ammunition in the U.S. military and delivers exceptional battlefield performance. The bullet usually yaws after impact and fragments, causing debilitating wounds. Mk 262 is lacking in the barrier penetration department, construction and mass being the limiting factors.

“Amongst all the scuffling and shouting, the 5.56 is a very good and effective caliber,” Alexander said. “How many .308s win at Camp Perry now? The 5.56 with a correctly constructed bullet is a very useful round, but the 6.5’s big advantage is delivering twice the material and energy to the target and greatly limiting wind drift.”

Most M14 rifles, coated in Cosmoline and stored away in the 1960s, had their wood stocks replaced with modular chassises that more readily accepted optics and other aiming, infrared illumination devices, etc. Accuracy tweaks and optics with a 10X top end were added before shipping overseas. When paired with 175-grain M118LR ammo, infantrymen armed with the M39 Enhanced Marksman Rifle (USMC), MK14 (NSW), or Enhanced Battle Rifle (Army) were good out to 1,000 yards depending on conditions. The 7.62mm round was, and is, obviously more lethal and penetrated barriers better than the 5.56.

The big disadvantages to the M39/EBR are its special ammo (or at least ammo not common to the average rifleman), magazines, and weight.

Retrofitting rifles is expensive and time consuming, and finding spare parts for a rifle that has not been in regular service for 50 years was a challenge at times.

The M110 SASS has been very well received by troops, mostly because of its semiautomatic capability. The fact that it runs almost exactly like its M16 little brother certainly doesn’t hurt. But it is heavy, heavier than the M16 at least, and still has the same oddball magazine and ammo requirements like the M39/EBR.

A DMR rifle in 6.5 Grendel with the right bullet solves most of these problems without giving up much in terms of downrange performance (see the accompanying charts). Alexander suggested an off-shelf solution in the form of Lapua’s 123-grain Scenar HPBT. Out of a 20-inch barrel the bullet would be pushing 2,600 fps with a .527 BC—the M118LR’s 175-grain MK has a BC of .505—so it doesn’t have to start out very fast to be effective downrange. Marksmen also gain five rounds, up to 25 from 20, by going Grendel instead of 7.62.

“Since most DMR rifles are equipped with 20-inch barrels, it makes sense to keep that length,” Alexander said.

“That barrel length generates enough velocity to stay supersonic out to 1,200 yards with the Scenar.”

Like the M16-based DMR rifles, both the Grendel infantry carbine and DMR would use the same magazines, same parts, and in a pinch the same ammo. The big advantage is 7.62-like lethality in a lightweight rifle. Grendel carbines and DMR rifles actually weigh a few ounces less than 5.56mm guns because the bore is bigger and there is less barrel steel to tote up the hill. Logistics guys and armorers would probably weep with joy to see the everything-is-different EBRs boxed up and salted away. Infantrymen would appreciate a rifle that is a couple of pounds lighter than the M110.

Alexander pointed out a misconception about the Grendel. Some think the short case’s minimal taper makes it difficult to feed. In reality the case has adequate taper and feeds exceptionally well—even with the green lacquer coating that stops the 5.56. It provides very reliable select fire ability. The magazine is still a weak point for heavy military use, but improvements are being made.

“Probably the biggest penalty would be the extra weight it would take to match a 5.56mm round count,” Alexander said. “Since the Grendel runs at low pressures (MAP is 50,000 psi), steel cases are an option, and that would help negate some of the weight gain.”

Refit
What would it take to convert millions and millions of M4 and M16 rifles to 6.5 Grendel? In theory, just a barrel, a bolt, and a magazine. The cartridge produces more recoil than the 5.56, but not so much more that it requires a new buffer or scope/accessory mounts.

“Probably the easiest and least expensive route would be to buy new uppers,” Alexander said. “Sure, you could swap barrels and bolts, but by the time you paid an armorer to do the work, the upper is probably the best route.”

The 14.5-inch upper runs $650 without rail, and the DMR upper runs $820, retail. If the U.S. military took the plunge and switched, these prices would obviously come way down. (A brand-new M4 runs just over $700.) But there is more to it than swapping rifles. All the supporting industries, namely ammunition manufacturers, would have to spin up production lines. And there is the issue of all that 5.56 and 7.62 ammo and the accompanying magazines sitting in storage depots around the world. A wholesale swap to 6.5 Grendel would cost billions of dollars.

History Repeating Itself
The British Army’s Land Pattern Musket, or Brown Bess, debuted in 1722 and was the infantry’s primary rifle for more than 100 years. There were dozens, if not hundreds, of incremental changes to improve its performance. But for the most part, its flintlock ignition and caliber remained unchanged. Ordnance officers felt that a new system that only marginally increased the musket’s battlefield performance simply was not worth the cost.

As it stands, the M16/M4 in 5.56x45mm is a good system that has been greatly improved over its 50-year service life. Sights, ammo, magazines—everything has been upgraded, and the rifle is accurate and reliable. Even though the 6.5 Grendel cartridge is far more lethal and has the potential to completely replace two different calibers and a dozen firearm systems, it still would offer an incremental increase in performance and therefore will probably never be issued to soldiers and marines headed into combat.

The same could have been said about the M16, too, right up until the moment a Colt salesman put one in the hands of General Curtis Lemay.

Alexander would neither confirm nor deny that rifles chambered in 6.5 Grendel had been requested or tested by the U.S. military. And since Alexander is being so tight lipped, only time will tell if the Grendel will ever become the next U.S. military service round.

The 6.5 Grendel (center) has a five-round magazine capacity advantage over the .308/7.62 (right), but gives up five rounds to the .223/5.56 (left).

I guess you don't know what MOA stands for. Look it up and report to the editor and chief, then look at the 6.5 mm Grendel article – look at the comparison charts under "DROP" and "WIND DRIFT" . Think about what you see there. At a 1000 yards the bullet drifts how far in a 10 MPH full value? And all the other distances recorded here are of the same problem.
If I'm wrong give me Hell.
Thanks — Tom

Tom Patterson

I guess you don't know what MOA stands for. Look it up and report to the editor and chief, then look at the 6.5 mm Grendel article – look at the comparison charts under "DROP" and "WIND DRIFT" . Think about what you see there. At a 1000 yards the bullet drifts how far in a 10 MPH full value? And all the other distances recorded here are of the same problem.

DetroitMan

In spite of the praise heaped on it, the 5.56mm cartridge is the worst part of a weak weapons system. Low weight and high accuracy do not make up for its shortcomings. The argument "the 5.56 wins at Camp Perrry" is laughable. It lacks lethality. The Army and Marines have tacitly admitted this by training troops to put two or three bullets in the target. That, by the way, completely negates the advantage of being able to carry more ammo. A more potent cartridge such as the Grendel would serve our troops much better.

It's also time to say goodbye to the M16/M4 platform. A rifle that must be torn down and cleaned every single day because dust can foul it is not a suitable military arm. The M1 and M14 didn't need that kind of babying, and neither should our current rifle. The M16 did its job in Vietnam, but better designs exist now. A less problem-prone rifle that doesn't need a new ammunition spec every few years should be a significant enough improvement. It's time we got serious about arming our soldiers with the best available rifle and cartridge.

LRRPF52

The 5.56 is actually a great cartridge, and is quite lethal, despite what you may have read. It's excellent for the close-range fight, and allows units to have more combat endurance than they would with 7.62×39 or 7.62 NATO. To state that training troops to put 2 or 3 bullets in a target is a tactical admission of the inferiority of a certain caliber shows how very few people understand the nature of close combat when making such claims.

Whether I'm shooting someone with a 7.62 NATO, AK, or 5.56 NATO service weapon, I'm going to place a rapid string of well-aimed fire into their chest and face as fast as I can on SEMI, then assess for follow-on shots. The caliber differences in these is nowhere near enough to have the effects you might expect them to, especially at close range. This is why 5.56 makes a lot of sense, because I can carry more of it, I can run rapid strings accurately and faster than you ever will with 7.62 NATO or short, and contrary to the BS about lethality, everyone I have seen take 5.56 suffered some pretty brutal wounds that always meant they either died within seconds, or were severely injured and out of the fight.

As to needing to clean the M16 family daily, that's another myth propagated by those who don't know. Keep them lubed, and they run. The system actually works better when fouled with carbon, as you get a better gas seal in the bolt carrier-to-bolt tail chamber.

Where the Grendel would really make a huge difference for us is if we could get a Light Machine Gun chambered in it to replace 7.62 NATO, and our SASS weapons as well. That would cut soldier's load and ammunition bulk profile for those who carry 7.62 NATO currently, without sacrificing downrange capability.

The problem is convincing the Pentagon and NATO to replace 11 years worth of 7.62 NATO logistical stockpiles, and field an LMG that will run on Grendel.

DetroitMan

Respectfully, I don't think we should focus on close range combat at the expense of all else. We also cannot rely on getting two or three hits in all combat conditions, especially as range increases. Regarding the M16, my buddies were deployed multiple times, and ordered each time to clean it daily. The requirements are no myth. Neither are the problems. The M4 finished dead last in reliability in the Army's most recent tests at Aberdean. It had more than three times as many stoppages as its nearest competitor.

The fact is, the 5.56 and the M16 both date to theories and technology of the 1950s. Things have advanced significantly since then. The military should take an honest look at new rifle technologies. They should stop expecting a giant leap, because it isn't realistic. The 6.5 Grendel is one technology that offers real, proveable advantages over the 5.56. It comes with only a mild increase in weight and recoil, and can double the effective range of the soldier's weapon. We have the money. Our military spends billions every year on experimental programs that don't pan out. I think cutting one or two of those programs to equip our troops with a better rifle would be worthwhile.

Bubba

Exactly’ or use some of that money the Government saved from not negotiating with terrorist .

MenotYou

Ever fire blanks out of a M4? One round will foul up your gun more than going 6 months without cleaning out the dust. Many rounds are fired during training without cleaning. To say you have to clean it daily because dust will cause it to malfunction is an exaggeration. Your “buddies” being ordered to clean their rifles daily does not mean if the did not the weapon would of malfunction because it was not cleaned the day before. Most malfunction usually result from worn out magazines anyway. This is coming from a combat veteran not from “my buddies”.

MURRAY

ITS A GOOD SUB MACHINE GUN ROUND THEN! UNFORTUNATELY WHATS COMING THE OTHER WAY IS RIFLE AMMUNITION, GET REAL.

Bubba

“This is why 5.56 makes a lot of sense, because I can carry more of it,……” Yes you would have to carry more of it if you are using three times as much of it.

Tanstaafl2

As an Alexander myself (not related to the owner – though I sometimes amuse myself wondering if it would raise any eyebrows should I submit a resume to them), I've always been interested in their offerings (having gone to school almost next door at Virginia Tech didn't hurt either).

The .50 Beowulf makes a great hog gun, but its ballistics pretty much limit it to brush gun ranges. The 6.5 Grendel looks to fill the role of a mid-power do-all cartridge pretty well. Now if only MacArthur hadn't put the kibosh on the .276 Pedersen cartridge, we'd have had a very similar cartridge to the 6.5 Grendel 80 years ago and would still be using it today.

http://twitter.com/Lakan_Kildap @Lakan_Kildap

correct.

MacArthur wasn't alone though, Hitler also curtailed development of intermediate powered rounds because he was thinking about those millions of stockpiled 7.92x57mm rounds.

The real blame goes to the US military brass who insisted on .30-06 performance when NATO standardized in the 1950's. The US vote won and thus was born the 7.62×51. Had the Pedersen been adopted in 1936, or the British .280 (7×43) in the 1950's, NATO's Cold War battle rifles would have been more controllable in full auto fire, and we might still be using them today.

Instead, we had the M16 and 5.56.

Jason B.

i think we need to see 50+ round surefire grendel mags. then we wouldnt see most of the pushback we get from the pro 5.56 community. i also think that you should be able to link them together side by side(not with ducttape that's just ghetto) for a faster first mag change.
PS. Love this article will be subscribing to shooting times now

LRRPF52

Only problem is the Surefire quad stack mags are unreliable, just as every quad stack design to-date has been, starting as early as the Suomi Kp31 9mm SMG. Coffin mags were banned by the Finnish Army for use on the Russian front from 1939-1944, as they are worthless.

My first time trying the SF60, it malf'd on me. Coffin mags simply don't work, and nobody has cracked the code to get them functional.

Clamping the Surefire quad mags together would be a bulky and impractical affair, even if they were reliable.

Charles

Imitation is the highest form of flattery. The Russians have fielded an intermediate cartridge for nearly 30 years. Then in 1974 they didn't turn to the 6.5 Grendal, or the 6.8 SPC, or any 300 Blackout. They copied what worked and came up with the 5.45mm. The 5.56mm is an outstanding general purpose cartridge. It might not be optimal in its present configuration or with the rifle system that is presently used, but if the "enemy" sees fit to copy your idea then it is probably not a bad idea.

Kevin

I know this issue has been referred to in both the article and the comments, but we can't overemphasize the importance of the "NATO" designation placed before these calibers. A remarkable thing about our current family of ammunition is its commonality accross nearly every state we have alliance arrangements with; a rare accomplishment in military history. The rounds and (usually) the magazines will work in our weapons or theirs, which GREATLY simplifies logistical planning in the event of either a major conflict or during coalition operations in places like Afghanistan. Common ammunition greatly diversifies the sources of supply, can shorten lines of supply, and increases our ability to both give and receive assistance. This extends from Corps level logistical planning down to two riflemen cross-leveling magazines on the battlefield. If we change, we disconnect ourselves from this system. Some of our allies will gradually change along with us, but few can afford the massive expense of transitioning. Losing this commonality and the logistical advantages it provides is an enormous hidden expense within a transition that would provide only marginal improvements in leathality.

DetroitMan

In practice it hasn't worked that smoothly. To this day some NATO countries load their 5.56mm ammunition in a way that increases stoppages in the M4 / M16. Some also believe that US bullets, which tend to fragment, are not in compliance with the Hague Convention, and therefore unsuitable for their own armed forces.

Our allies were never particularly fond of the 5.56 or 7.62 NATO. Most wanted an intermediate cartridge in the 6.5 to 7 mm range. They grudgingly accepted the 7.62 in the 1950's. Many rejected the 5.56 initially and kept the 7.62 into the 1980's. They might actually be happy if we adopted an intermediate cartridge in the 6.5 to 7 mm range.

Lastly, our allies are big boys and NATO has largely outlived its usefulness. They are free to follow us or not. We still produce vast quantities of 5.56 / .223 for the civillian market because it's popular, and that won't die anytime soon. If we ever had to supply them with 5.56 ammo in a war, our industry can handle it.

Bubba

Following that logic then NATO should have been using the 7.62 X 39 to diversify the enemies’ supply as well when ever possible…. but still maintain the advantage by firing it from a more accurate platform.

Robert

First, I dont claim to know a ton about weapons or ammunition, but i am a very common sense person. I say that so you know this isn't so much of a "technical analysis". In an earlier comment one posted that the 5.56 round is great at short range. The mililtary obviously believes it to be a suitable round or they wouldnt be using it. My way of thinking is with the Grendel in short range situation, at minimum, you have a slightly more lethal round, great. But you've also got the huge benefit, in my opinion, of the significant extra range. You don't have to wait until the enemy gets so close before you squeeze off a couple. Depending on scenery, you have the opportunity to fire before he is within his weapons range therefore, an advatage. As the article said, you would be limited by optics etc. instead of the rounds limitation. Although I'm not sure it would be a big enough difference to spend the money to convert.

Klaus

Does anyone know where I can get a 6.5mm Grendel weapon that looks like the Colt M4 police version. It is a LE6920 M4 with the magpul accessories.

Josh

Being a 6.5 grendel owner. I can tell you that this would make a good battle rifle. Although slower muzzle velocities than the 5.56. The very high bc of the 6.5 bullets make up for it. Mine was built by J&T distributing.

marvin

why has no one else, other than the first poster commented on the tables in this article? the bc’s are being used incorrectly/inconsistently i believe. the m855 bullet drops are just plain wrong.

Chris

In my opinion weighing the ballistics, cost per round, weight of the weapon, cost of the weapon, lethality I give this round as high of a mark as possible. In reality this round should do to the 5.56 what the .17 HMR has done to the .22 . The SPC is also a step up but I would compare the difference to the same scenario played out with the HMR and Mach2. The better round will win…that is hands down the Grendel.

SGT USMC RECON

Bubba

Lots of talk about the 6.5’s weight savings and more number of rounds carried and lethality but the point is accuracy. First you have to hit the target before any of those other things matter. If it is a more accurate round then it would be a crime not to instate it after all that is the most impotant part of the mission……hit the target.

bob

The grendel performs almost as well as my .308 with very little recoil. It is my hunting rifle on ar platform and I took a 350 russian boar with one round. A shoulder shot at 70 yards went clear through.

Godzilla

“Soldiers are having trouble dominating the battlefield past 300 or 400 yards.”

“I finally came right out and asked developer Bill Alexander if he thought the Grendel would ever get a shot at replacing the much-maligned 5.56x45mm NATO cartridge.”

Everytime you go with a bigger round, you have to compromise with shorter distance and/or more recoil! You cant have everything for the price of one. The 6.5 grendel seems to split the power/distance/recoil factors between the 5.56 and 7.62 and thus is a great intermediate round.

But lets not denigrate the 5.56 nato round undeservedly. More distance, less recoil, lighter backpacks, lighter rifles, etc makes for a more practical and desirable platform 90% of the time.

alfred montestruc

My thought is that, not necessarally the KEL-TEC RFB, but a weapon very much like it in 6.5 Grendel would be a major improvement. It is an ambidextrous bullpup that ejects downward. The slide is long to allow the weapon to eject down, which also gives a much softer recoil.

This weapon is now in late prototype stages, and has only been made in 5.56mm, but the potential seems obvious. With a bullpup configuration you gain ~ 5-6 inches of barrel for the same length of weapon, this would allow a compact 6.5 Grendel with a 30+ inch barrel. At least a very interesting concept.